An antenna can be any conductive structure that can carry an electrical current. Antennas are generally used to receive or transmit a signal, with the overall design and capabilities of the antenna being a function of the antenna's intended use. Antennas can be designed to receive or transmit signals in all directions, and such devices are referred to as omni-directional antennas. Directional antennas are also commonly used, and are generally used to receive or transmit a signal in a specific direction, or field of view. Directional antennas are designed to provide a higher gain for the signal verses omni-directional antennas. The added gain provided by a directional antenna is useful (and often necessary) in many antenna applications, and hence techniques are continually being developed to enhance the directional capabilities of such antennas, as well as the overall gain provided in relation to such directionality.
In the field of directional antennas there exist today various devices that can produce high gains and/or readily switchable directionality. However, tradeoffs often exist between the capabilities provided. For instance, mechanically driven devices can be designed to produce a very high gain. The most common example would include a dish antenna (i.e. parabolic or otherwise) that is driven by a mechanically steerable device. Such dish antennas are generally large relative to other types of antennas, and the steering system is usually complex. Moreover, the overall system using the device will need to provide enough clearance around the antenna for its physical movement across a range of directionality.
Other devices exist which can provide directionality of the antenna via electronic switching. Examples of such would include "smart" scanned patch array antennas, active element arrays, and the like. Such devices can be designed to provide sufficient gain for certain applications, and will also provide limited directional scanning. However, these devices usually require complex phase shifting electronics to provide beam steering.
Still other devices exist which can provide relatively higher gains, along with directionality. Examples of such devices would include Yagi antennas, unscanned patch arrays, and the like. The Yagi antenna is an example of a fairly high gain array where most of the elements are fed parasitically from one or more driven elements. The Yagi is a relatively inexpensive antenna as the feed network is fairly simple, but dimensional adjustments may be critical in its design and implementation. The phase in the parasitic elements, as used to control the array factor, is controlled by adjusting the lengths and spacings of the elements. This combination of adjustment parameters can be important. The bandwidth of a Yagi antenna is usually only a few percent, yet the antenna can provide a fairly high gain considering its electrical size. The directionality, however, is not generally variable without turning the configured antenna in one direction or another.
Another type of antenna design can provide scannable 360-degree coverage, via electronic switching and the like, between the various elements comprising the antenna. Such antennas generally provide for less gain, and also require more complex switching and feed networks. An example of such an antenna is disclosed in U.S. Pat. No. 5,479,176 issued to Zavrel. Zavrel is characterized by eight electronically switchable radiating directions, with pairs of radiators being used to form parasitic elements, driven elements, and reflectors. Certain drawbacks of Zavrel include its switching complexity, and also its lack of gain on the horizon. For instance, in a useful network, a subscriber terminal (equipped with an antenna) must generally provide 12-18 dBi of gain on the horizon. The antenna of Zavrel only provides approximately 13 dBi of gain at 5 degrees above the horizon, and only 10 dBi of gain on the horizon. The Zavrel array also requires multiple feed points to achieve its gain. This requires splitting the input energy into a minimum of four (4) paths, which incurs an additional system loss. This system loss might range from approximately 2-4 dB, depending upon other factors such as thermal loss, and the like. Thermal loss might amount to 1 dB per switch tree level. Hence a 4-way split such as Zavrel might have would incur approximately 2 dB (or more) of losses, as it uses two (2) divider levels. Thus, in terms of useful gain, the Zavrel array only provides 6-8 dBi of gain.
Zavrel provides certain improvements in wireless network capacity versus terminals using a low gain omni-directional antenna. However, the order of magnitude of improvement in capacity and performance which might be required to justify the substitution of a more complex and expensive directional antenna is not provided by Zavrel. A network operator could not likely justify substitution of a more complex and costly directional antenna for a simple omni-directional monopole antenna unless higher gain can be economically provided.
Accordingly, what is needed in the field of art is an electrically scannable directional antenna with a higher useful gain, particularly on the horizon. The antenna should have a scanning ability with 360 degrees of coverage, fast switching between beam positions, directional self-alignment, and provide for relatively simple installation by a user. The antenna should also provide for alignment control commands that can be provided by an associated command device, or via over-the-air alignment commands, and which results in alignment of the antenna device without mechanical adjustments.